Clinical Value of Visual Acuity

Visual acuity is defined as the clarity or sharpness of vision measured at a distance of 20 feet.¹ Typically, the clarity of vision is measured by the ability to distinguish different sized letters or shapes at a fixed distance, usually with a Snellen chart.² Normal visual acuity is rated as 20/20 vision.^1,2 Visual impairment is defined as acuity less than 20/60, and blindness as visual acuity worse than 20/400.^3,4

In dentistry, optimal visual acuity is vital for patient assessment and treatment. It is imperative to have a clear and focused field of vision to be able to assess oral tissues, accurately evaluate periodontal measurements, review radiographs, and detect and treat oral disease. Dental professionals are at risk for increased eyestrain and reduced visual acuity over the course of their careers due to the influence of age on vision, and the increasing use of technology — which is a common source of digital eyestrain.^5,6 Thus, oral health professionals should be aware of visual acuity changes that can occur throughout their lifetime, and make necessary adjustments to maintain optimal clinical performance.

CAUSES OF VISUAL IMPAIRMENT

Visual impairment increases substantially with age.⁴ Presbyopia is an age-related condition in which the eye gradually loses the ability to focus on nearby objects.⁷ A refractive error of the eye, presbyopia indicates the eye does not correctly bend light, resulting in a blurred image.⁸ Other refractive errors include myopia (nearsightedness), hyperopia (farsightedness), and astigmatism (asymmetric cornea curvature).⁸ Refractive errors can be easily diagnosed and measured, and corrected with glasses to attain normal vision.⁹ If they are not corrected or the correction is inadequate, however, refractive errors become a major cause of reduced vision and blindness.^3,4

In the provision of care, dental providers need the visual acuity to focus on the oral cavity at short distances (27 to 50 cm).¹⁰ Moreover, the eye must be able to quickly accommodate (that is, change focus) to an intermediate distance (e.g., 40 to 90 cm) as providers shift their gaze to instruments, records and radiographs on a table or computer screen.¹⁰ However, refractive errors may impede the clinician from visually adapting — and, thus, optical assistance may become necessary.¹⁰

STRATEGIES TO IMPROVE VISUAL ACUITY

The most common occupational hazard in dentistry is eyestrain.¹⁰ Research shows that 87% of dentists will experience some type of eyestrain, and 90% will require visual assistance at some point.¹⁰ Visual deficiencies can be compensated with the use of optical magnification aids, such as loupes. Galilean loupes are common in dentistry, with magnification ranging from 2.5x to 3.5x, and an adjustable working distance to meet the clinician’s ergonomic needs.^5,11 Galilean loupes, however, offer a limited field of view.

Conversely, Keplerian or prismatic loupes allow for various magnifications and working distances, with a preferred range of 3.5x to 6x, yet they are heavier and more expensive than Galilean loupes.^5,11 According to Perrin et al,¹¹ when choosing loupes there is a trade-off between optics and ergonomics. Galilean loupes offer mainly ergonomic advantages for younger clinicians and compensate presbyopia in clinicians older than 40.¹¹ In comparison, the Keplerian loupe facilitates better detail detection in all age groups.¹¹ Also, a new type of loupe is available that claims to provide 3.5x magnification with a large field of view.

ANGULATION AND ILLUMINATION

The angulation and alignment of loupes must be custom fit to the clinician to effectively prevent eyestrain. Additionally, illumination is an important factor, as enhanced illumination increases both depth of field and visual acuity.^5,11 Although oral health professionals with presbyopia can compensate by using magnification, they may not be able to achieve the same visual acuity as they had in their youth.^5,11

Today, with increasing use of technological devices, many individuals experience symptoms of digital eyestrain.⁶ Nearly 80% of Americans report using digital devices for more than two hours daily, and 59% attest to experiencing digital eyestrain.⁶ The most common indicators of digital eyestrain are headaches, dry eyes, blurred vision, and neck and shoulder pain.⁶ Increasingly, oral health professionals are using digital technologies and devices when treating patients. Digital radiography, intraoral scans, electronic health records, and prescription and insurance databases are used in the dental team’s day-to-day functions. The combined use of these technologies in dental settings increases screen time, which may raise the risk of digital eyestrain.

To alleviate digital eyestrain, special eyewear — including contact lenses with magnification, and eyewear with blue-light filtering and antireflective capabilities — is recommended.⁶ Additional solutions for reducing digital eyestrain include reducing overhead lighting to decrease screen glare, increasing text font sizes, taking frequent breaks, and maintaining proper viewing distance from the digital device.⁶ Oral health professionals should have near vision tested regularly, and discuss their digital activities with an eye care provider to relieve eyestrain and support visual acuity.

The addition of loupes in oral health curricula should be considered, as their use may enable students to better assess clinical details, as well as the overall oral health status of patients.¹² Although loupes are being used in private practice to improve ergonomics and enhance visual acuity, they are not always routinely implemented in dental educational programs.¹³

In the dental office, research suggests injuries caused by musculo­skeletal disorders can be minimized or prevented with the use of appropriate equipment, including loupes and illumination. This combination can also reduce cognitive and physical stress by creating a safe, healthy and comfortable workspace for dental teams. Additionally, the early incorporation of magnification may help diminish the inevitable decline in vision over time.¹³

CONCLUSION

Using magnification aids, such as loupes, can reinforce proper ergo­nomics, improve musculoskeletal health, and reduce eyestrain. Taking steps to support visual acuity over a clinician’s lifetime can enhance physical health and lead to longer, more productive careers.¹²

The influence of age, eyestrain, and leading causes of visual impairment can compromise detail detection and clinical precision.^3,4,11 Thus, oral health professionals should be aware of — and willing to consider — methods to compensate for visual deficiencies. The timing of adoption is also an important consideration, as Maillet et al¹⁴ report that early use of magnification not only enhances visual acuity, it also supports effective ergonomic practice over the course of the clinician’s career.

KEY TAKEAWAYS

• Research shows that 87% of dentists will experience some type of eyestrain, and 90% will require visual assistance at some point.¹⁰
•  The angulation and alignment of loupes must be custom fit to the clinician to effectively prevent eyestrain.
• Additionally, illumination is an important factor, as enhanced illumination increases both depth of field and visual acuity.^5,11
• The timing of adoption is also important, as early use of magnification not only enhances visual acuity, it also supports effective ergonomic practice over the course of a career.

REFERENCES

1. American Optometric Association. Visual Acuity FAQs. Available at: aoa.org/​patients-and-public/​eye-and-vision-problems/​glossary-of-eye-and-vision-conditions/​visual-acuity/​visual-acuity-faqs. Accessed December 15, 2020.
2. Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health. Visual Acuity. Available at: https:/​/​medical-dictionary.thefreedictionary.com/​visual+acuity. Accessed December 15, 2020.
3. Resnikoff S, Pascolini D, Mariotti SP, Pokharel GP. Global magnitude of visual impairment caused by uncorrected refractive errors in 2004. Bull World Health Organ. 2008;86:63–70.
4. Sommer A. Visual impairment. Access Science. Available at: accessscience.com/​content/​visual-impairment/​734050. Accessed December 15, 2020.
5. Eichenberger M, Perrin P, Neuhaus K, Lussi A, Bringolf U. Influence of loupes and age on the near visual acuity of practicing dentists. J Biomed Opt. 2011;16:035003.
6. The Vision Council. The Vision Council Shines Light on Protecting Sight — and Health — in a Multi-screen Era. Available at: https:/​/​www.thevisioncouncil.org/​blog/​vision-council-shines-light-protecting-sight-and-health-multi-screen-era. Accessed December 15, 2020.
7. American Optometric Association. Eye and Vision Conditions. Available at: aoa.org/​patients-and-public/​eye-and-vision-problems/​glossary-of-eye-and-vision-conditions#presbyopia. Accessed December 15, 2020.
8. Kellogg Eye Center. Michigan Medicine. Refractive Errors. Available at: umkelloggeye.org/​conditions-treatments/​refractive-errors. Accessed December 15, 2020.
9. The World Health Organization. Blindness and Vision Impairment. Available at: who.int/​en/​news-room/​fact-sheets/​detail/​blindness-and-visual-impairment. Accessed December 15, 2020.
10. Burton JF, Bridgman GF. Eyeglasses to maintain flexibility of vision for the older dentist: the Otago dental lookover. Quintessence Int. 1991;22:879–882.
11. Perrin P, Eichenberger M, Neuhaus KW, Lussi A. Visual acuity and magnification devices in dentistry. Swiss Dent J. 2016;126:222–235.
12. Congdon LM, Tolle SL, Darby M. Magnification loupes in U.S. entry-level dental hygiene programs — occupational health and safety. J Dent Hyg. 2012;86:215–222.
13. Arnett M, Gwozdek A, Ahmed S, Beaubien H, Yaw K, Eagle I. Assessing the use of loupes and lights in dental hygiene educational programs. J Dent Hyg. 2017;91:15–20.
14. Maillet J, Millar M, Burke J, Maillet M, Maillet W, Neish N. Effect of magnification loupes on dental hygiene student posture. J Dent Educ. 2008.72:33–44.

The authors have no commercial conflicts of interest to disclose.

From Decisions in Dentistry. January 2021;7(1):18,21.